The present invention relates to directional drilling, particularly to a sonde housing structure for use with a directional drilling bit.
Directional drilling is used for boring under or through obstructions such as roadways, concrete lined waterways and large underground utilities to provide a passageway for utility lines without the need for trenching through or excavating around the particular obstruction. This need has been met by the development of a variety of systems for the installation of underground conduits and pipe bursting/replacement systems.
Directional boring apparatus for making holes through soil are well known. The directional borer generally includes a series of drill rods joined end to end to form a drill string. The drill string is pushed though the soil by means of a powerful device such as a hydraulic cylinder. The drill string ends in a bit having a sloped front face that causes the bit and drill string to deviate in the direction of the sloped face in order to steer. The bit may be pushed and rotated and the same time in order to drill straight. See McDonald U.S. Pat. No. 4,694,913, issued Sep. 22, 1987. A spade, bit or head configured for boring is disposed at the end of the drill string and may include an ejection nozzle for water to assist in boring.
Accurate directional boring necessarily requires information regarding the orientation and depth of a cutting or boring tool. Consequently, a sensor and transmitting device (xe2x80x9csondexe2x80x9d) attached to the cutting tool is normally required to prevent mis-boring and re-boring. See, for example, Mercer U.S. Pat. Nos. 5,155,442 and 5,633,589. The sonde includes electronic and electromagnetic components that are sensitive to vibration and may fail if subjected to excessive vibrational shock in service. Since the sonde needs to be positioned adjacent to the cutting or boring head in a drill string in order to provide accurate information regarding the orientation of the cutting head, any vibrations or shock may result in premature failure of the sonde. Additionally, a sonde used in directional boring needs to be housed in a manner that facilitates easy access while simultaneously providing adequate protection to the device.
Sondes have been located inside of a bit assembly, such as shown in Stangl U.S. Pat. No. 4,907,658. More typically, however, the sonde is located in a tubular housing that can be connected and disconnected from the housing. The sonde itself is loaded into a compartment that is isolated from compressed fluid that is supplied to the bit through a separate passage in the sonde housing. See Wentworth PCT Publication No. WO 00/11303, published Mar. 2, 2000, and Cox U.S. Pat. Nos. 5,950,743, 5,934,391, 5,931,240 and 5,899,283 for side load sonde housings wherein a door or cover for the sonde compartment is provided.
End load sonde housings are also known wherein the sonde is loaded into a blind hole at the rear end of the sonde housing, which is then coupled to a trailing component such as a starter rod. A spacer is inserted behind the sonde to hold it in place. These designs avoid the possibility of breakage of a side load door, but replacing the sonde requires disassembly of drill head.
One known side loading sonde housing design is described in commonly-assigned U.S. Pat. No. 6,148,935 and U.S. Pat. No. 6,260,634, the entire contents of which are incorporated for all purposes by reference herein. These patents describes a coupling system known commercially as Splinelok(trademark) wherein the starter rod is connected to the rear end of the sonde housing by a series of interlocking splines that pass torque from the drill string to the sonde housing and bit attached to the front end of the sonde housing.
All sonde housing designs must provide sufficient space for the sonde cavity and for a fluid passage to pass drilling fluid up to the bit, which fluid passage is isolated from the sonde compartment, while maximizing the strength of the housing. The sonde is either battery powered or connected to the surface by a wire which runs through the drill string (xe2x80x9cwirelinexe2x80x9d).
A need persists for a sonde housing that provides for increased security and protection of the sonde while simultaneously affording convenient and rapid access to the sonde. The present invention provides an end load sonde housing system that is easier to access than known end load systems.
According to the invention, an apparatus for mounting an electronic device therein for use in an underground boring machine includes an elongated housing having an elongated, lengthwise central cavity opening at one end thereof. A cartridge containing a sonde fits in the cavity. A keying mechanism is provided on the cartridge and sonde, and also between the cartridge and the housing, for securing the cartridge and sonde in a predetermined orientation relative to the sonde housing when the cartridge is inserted into the cavity through the opening. The sonde housing also preferably includes a lengthwise fluid passage therein which is isolated from the cavity containing the cartridge. According to preferred forms of the invention, an end cap or plug is also provided which holds the sonde cartridge in its installed position and isolates it from contact with the pressure fluid in configurations where the fluid passage and cavity branch from a common end opening of the housing.
A drill head for use in directional drilling according to the invention includes an elongated housing having an elongated, lengthwise central sonde cavity opening at a front end thereof, a keying mechanism for securing the sonde in a predetermined orientation relative to the housing when the sonde is inserted into the cavity through the opening, a closure device for enclosing the cavity with the sonde therein, and a bit assembly mounted at the front end of the sonde housing, such that upon removal of the bit assembly, the cavity containing the sonde can be accessed. Preferably the sonde is contained within a cartridge as described below. A drill string may be directly connected to a rear end of sonde housing without need for an adapter or starter rod. Preferably fluid passages conduct a pressure fluid through the sonde housing to its front end to further fluid passages in the bit assembly. In this arrangement, the closure device comprises a cap which seals the cavity from the pressure fluid, whether or not the cap forms part of a cartridge for the sonde.
A sonde cartridge according to the invention comprises a tube sized to closely receive a cylindrical sonde therein, the tube having alignment openings therein whereby a pin can be used to secure the tube against movement relative to a sonde housing in which the cartridge is to be installed, an end cap which fits into one end of the tube, a keying device which can engage a notch in the sonde so that the sonde may be installed in a predetermined position within the cartridge, and a fastener for securing the end cap to the tube.
The present invention provides an improved end load sonde housing that is inherently stronger than conventional side load configurations and which provides a nonthreaded mechanism for indexing and maintaining the sonde in the proper clockwise position, thereby minimizing the possibility of misboring.